In a letter to The Daily Telegraph, 90 QCs condemn as “unjust” the government’s proposals to restrict the judicial review process and suggest that “conscientious and dedicated” public law firms will be driven out of business.

Mr Grayling announced last month that applications for judicial review - the process by which judges are asked to examine the legality of government decisions - will only receive legal aid funding once a judge has agreed the case is strong enough to proceed to a full hearing.

He said it was designed to weed out “weak” cases by forcing lawyers to “stop and consider” the strength of their application.

“We are gravely concerned that practical access to justice is now under threat,” the letter says.

“The cumulative effect of these proposals will seriously undermine the rule of law, and Britain’s global reputation for justice.

“They are likely to drive conscientious and dedicated specialist public law practitioners and firms out of business. They will leave many of society’s most vulnerable people without access to any specialist legal advice and representation.”

It adds: “We urge the Government to withdraw these unjust proposals.”

The letter point out that its signatories act both for and against the government in judicial review cases, and claims that “abuses” by British officials and agents overseas will now attract “impunity”.

This was thought to be a reference to cases such as the 2004 judicial review into whether British servicemen breached the human rights of 13 Iraqi civilians who died in the conflict, including Baha Mousa, a 26 year-old Iraqi man who died in British forces custody and whose family later received a £2.8 million payout.

The Justice Secretary said last month as he announced the plans: “I’m concerned that legal aid is being used to fund a number of weak judicial review cases, which incur costs for, public authorities and the legal aid scheme.”

He added: “Legal aid is not free money - it comes out the pocket of hard-working taxpayers. I hope this will make lawyers stop and more carefully consider the strength of any case for a judicial review.”

Last year 845 applications for judicial review - around half of them immigration cases - received initial public funding before being refused permission to proceed to a full hearing.

The proposed reforms are part of a wide-ranging package aiming to cut the £1.7 billion a year legal aid bill.

A Ministry of Justice spokeswoman said: "Judicial review is an important way of challenging decisions by public authorities, and we believe it should remain so.

"But we are concerned that legal aid is currently being used to fund a significant number of weak cases which have little effect other than to incur unnecessary costs for the taxpayer.

"Our proposal would not prevent legal aid being granted for future judicial reviews.”